Situational awareness is a vitally important element of battlefield survival. Nothing improves this awareness as well as clear, direct vision. However, this usually means the viewer, who is otherwise safely housed within an armored vehicle, for example, must be exposed to enemy ballistic and blast threats in order to have a view of the outside world. The dilemma of providing protection while permitting a clear view has been addressed in the past by providing an “armored window” in the vehicle. One common form of prior art armored window includes a frame spanned by a plurality of horizontal steel armor plates, which are vertically overlapping and spaced apart, with the inner and outer surfaces of each plate coated with a reflective material to form a short periscope. In other words, the viewer does not see an image directly, but instead sees the image reflected twice, once off the outer surface of one plate and then the inner surface of the plate immediately above it. This type of armored window has been used in armored personnel carriers, such as the Bradley Fighting Vehicle, and is called the TRAPP (Transparent-Armor Piercing Protection) Armor System, the design of which is disclosed in U.S. Pat. No. 5,452,641.
The TRAPP Armor System is an arrangement of front cover plate, back plate or “catcher,” a plurality of angularly mounted parallel steel plates separated by an air space and a frame that holds the assembly together. The facing sides of the parallel plates are ground, polished and plated to achieve a mirror finish. When an image is viewed through the arrangement of plates, it is reflected twice and is seen erect and slightly offset as through a periscope.
The use of mirrored armor plates has a number of inherent drawbacks. The prior art armored window requires a reflective coating to be applied to the steel armor plates themselves. The application of such a coating is achieved by laminating a mirrored layer to each side of the armor plates, a process both difficult and expensive. Once the lamination is achieved, any separation between the plate and the mirrored layer, such as the formation of bubbles created by differential expansion rates due to heat extremes encountered in the field, will cause distortion of the image. Unless the mirrored surfaces are optically perfect, unacceptable distortions are introduced. Achieving this mirror finish is difficult, expensive, and hard to maintain on the steel plates.
While the system protects the occupants, the system is fragile. When fragments from bursting artillery rounds or small arms projectiles (bullets) strike the TRAPP system, the lines of flight are altered by the steel plates. The alterations in the line of flight can be dramatic enough to cause the fragment or bullet to impact two or more plates. The plate impacts tend to shatter the fragments and bullets and absorb their energy. Eventually the fragments and projectiles, with reduced residual energy, impact the backing plate where they are captured. As alignment of the plates is critical, these forces tend to skew a plate which reduces visibility and may open a path for later bullets or fragments. Thus the prior art design limits the ballistic protection to relatively low levels.
In the prior art, the space between plates provides no benefit and complicates the design because it requires the system to be hermetically sealed to prevent the free exchange of air laden with dust and moisture that will diminish the reflectivity of the plate surfaces. The reflective surfaces on the steel plates are difficult and expensive to apply, and are often subject to separation which causes image distortion. Moreover, the frame requires precision machining and is thus expensive to manufacture. The plates must be affixed within the frame so as to be parallel to each other in three dimensions in order for the reflected image to accurately represent what is outside the vehicle. Thus there is a need to overcome the deficiencies of the present armor system, to simplify and reduce the cost of construction, to increase ballistic performance, to improve the optics, to improve reliability, and to eliminate the need for hermetically sealing the system.